Sections 1.1-1.8 presented an overview of technology of computer networking and the Internet. You should know enough now to impress your family and friends. However, if you really want to be a big hit at the next cocktail party, you should sprinkle your discourse with tidbits about the fascinating history of the Internet [Segaller 1998].

1.9.1: Development and Demonstration of Early Packet Switching Principles: 1961-1972

The fields of computer networking and today's Internet trace their beginnings back to the early 1960s, a time at which the telephone network was the world's dominant communication network. Recall from Section 1.4 that the telephone network uses circuit switching to transmit information from a sender to receiver--an appropriate choice given that voice is transmitted at a constant rate between sender and receiver. Given the increasing importance (and great expense) of computers in the early 1960s and the advent of timeshared computers, it was perhaps natural (at least with perfect hindsight!) to consider the question of how to hook computers together so that they could be shared among geographically distributed users. The traffic generated by such users was likely to be "bursty"--intervals of activity, such as the sending of a command to a remote computer, followed by periods of inactivity while waiting for a reply or while contemplating the received response.

Three research groups around the world, all unaware of the others' work [Leiner 1998], began inventing the notion of packet switching as an efficient and robust alternative to circuit switching. The first published work on packet-switching techniques was that of Leonard Kleinrock [Kleinrock 1961, Kleinrock 1964], at that time a graduate student at MIT. Using queuing theory, Kleinrock's work elegantly demonstrated the effectiveness of the packet-switching approach for bursty traffic sources. In 1964, Paul Baran [Baran 1964] at the Rand Institute had begun investigating the use of packet switching for secure voice over military networks, and at the National Physical Laboratory in England, Donald Davies and Roger Scantlebury were also developing their ideas on packet switching.

The work at MIT, Rand, and NPL laid the foundations for today's Internet. But the Internet also has a long history of a let's-build-it-and-demonstrate-it attitude that also dates back to the early 1960s. J.C.R. Licklider [DEC 1990] and Lawrence Roberts, both colleagues of Kleinrock's at MIT, went on to lead the computer science program at the Advanced Research Projects Agency (ARPA) in the United States. Roberts published an overall plan for the so-called ARPAnet [Roberts 1967], the first packet-switched computer network and a direct ancestor of today's public Internet. The early packet switches were known as interface message processors (IMPs) and the contract to build these switches was awarded to the BBN company. On Labor Day in 1969, the first IMP was installed at UCLA under Kleinrock's supervision, with three additional IMPs being installed shortly thereafter at the Stanford Research Institute (SRI), UC Santa Barbara, and the University of Utah (Figure 1.28). The fledgling precursor to the Internet was four nodes large by the end of 1969. Kleinrock recalls the very first use of the network to perform a remote login from UCLA to SRI, crashing the system [Kleinrock 1998].

Figure 1.28: The first interface message processor (IMP), with L. Kleinrock

By 1972, ARPAnet had grown to approximately 15 nodes, and was given its first public demonstration by Robert Kahn at the 1972 International Conference on Computer Communications. The first host-to-host protocol between ARPAnet end systems known as the network-control protocol (NCP) was completed [RFC 001]. With an end-to-end protocol available, applications could now be written. The first e-mail program was written by Ray Tomlinson at BBN in 1972.

1.9.2: Internetworking, and New and Proprietary Networks: 1972-1980

The initial ARPAnet was a single, closed network. In order to communicate with an ARPAnet host, one had to actually be attached to another ARPAnet IMP. In the early to mid 1970s, additional packet-switching networks besides ARPAnet came into being: ALOHAnet, a microwave network linking together universities on the Hawaiian islands [Abramson 1970]; Telenet, a BBN commercial packet-switching network based on ARPAnet technology; Tymnet; and Transpac, a French packet-switching network. The number of networks was beginning to grow. In 1973, Robert Metcalfe's Ph.D. thesis laid out the principle of Ethernet, which would later lead to a huge growth in so-called local area networks (LANs) that operated over a small distance based on the Ethernet protocol.

Once again, with perfect hindsight one might now see that the time was ripe for developing an encompassing architecture for connecting networks together. Pioneering work on interconnecting networks (once again under the sponsorship of DARPA--Defense Advanced Research Projects Agency), in essence creating a network of networks, was done by Vinton Cerf and Robert Kahn [Cerf 1974]; the term "internetting" was coined to describe this work.

These architectural principles were embodied in the TCP protocol. The early versions of TCP, however, were quite different from today's TCPs. The early versions of TCP combined a reliable in-sequence delivery of data via end-system retransmission (still part of today's TCP) with forwarding functions (which today are performed by IP). Early experimentation with TCP, combined with the recognition of the importance of an unreliable, non-flow-controlled end-end transport service for applications such as packetized voice, led to the separation of IP out of TCP and the development of the UDP protocol. The three key Internet protocols that we see today--TCP, UDP, and IP--were conceptually in place by the end of the 1970s.

In addition to the DARPA Internet-related research, many other important networking activities were underway. In Hawaii, Norman Abramson was developing ALOHAnet, a packet-based radio network that allowed multiple remote sites on the Hawaiian islands to communicate with each other. The ALOHA protocol [Abramson 1970] was the first so-called multiple-access protocol, allowing geographically distributed users to share a single broadcast communication medium (a radio frequency). Abramson's work on multiple-access protocols was built upon by Metcalfe and Boggs in the development of the Ethernet protocol [Metcalfe 1976] for wire-based shared broadcast networks; see Figure 1.29. Interestingly, Metcalfe and Boggs' Ethernet protocol was motivated by the need to connect multiple PCs, printers, and shared disks together [Perkins 1994]. Twenty-five years ago, well before the PC revolution and the explosion of networks, Metcalfe and Boggs were laying the foundation for today's PC LANs. Ethernet technology represented an important step for internetworking as well. Each Ethernet local area network was itself a network, and as the number of LANs proliferated, the need to internetwork these LANs together became increasingly important. We discuss Ethernet, Aloha, and other LAN technologies in detail in Chapter 5.

Figure 1.29: Metcalfe's original conception of the Ethernet

In addition to the DARPA internetworking efforts and the Aloha/Ethernet multiple-access networks, a number of companies were developing their own proprietary network architectures. Digital Equipment Corporation (Digital) released the first version of the DECnet in 1975, allowing two PDP-11 minicomputers to communicate with each other. DECnet has continued to evolve since then, with significant portions of the OSI protocol suite being based on ideas pioneered in DECnet. Other important players during the 1970s were Xerox (with the XNS architecture) and IBM (with the SNA architecture). Each of these early networking efforts would contribute to the knowledge base that would drive networking in the 80s and 90s.

It is important to note here that in the 1980s (and even before), researchers such as [Fraser 1983, 1993] and [Turner 1986] were also developing a competitor technology to the Internet architecture. These efforts have contributed to the development of the ATM architecture, a connection-oriented approach based on the use of fixed-size packets, known as cells. We will examine portions of the ATM architecture throughout this book.

The architectural principles that Cerf and Kahn [Cerf 1974] articulated for creating a so-called "open network architecture" are the foundation on which today's Internet is built [Leiner 1998]: Minimalism, autonomy: A network should be able to operate on its own, with no internal changes required for it to be internetworked with other networks. Best-effort service: Internetworked networks would provide best-effort, end-to-end service. If reliable communication was required, this could be accomplished by retransmitting lost messages from the sending host. Stateless routers: The routers in the internetworked networks would not maintain any per-flow state about any ongoing connection. Decentralized control: There would be no global control over the internetworked networks. These principles continue to serve as the architectural foundation for today's Internet, even 25 years later--a testament to the insight of the early Internet designers. For an interesting retrospective look at the Internet design philosophy, see [Clark 1988]

1.9.3: A Proliferation of Networks: 1980-1990

By the end of the 1970s, approximately 200 hosts were connected to the ARPAnet. By the end of the 1980s the number of hosts connected to the public Internet, a confederation of networks looking much like today's Internet, would reach 100,000. The 1980s would be a time of tremendous growth.

Much of the growth in the early 1980s resulted from several distinct efforts to create computer networks linking universities together. BITnet (because it's their network) provided e-mail and file transfers among several universities in the Northeast. CSNET (computer science network) was formed to link together university researchers without access to ARPAnet. In 1986, NSFNET was created to provide access to NSF-sponsored supercomputing centers. Starting with an initial backbone speed of 56 Kbps, NSFNET's backbone would be running at 1.5 Mbps by the end of the decade, and would be serving as a primary backbone linking together regional networks.

In the ARPAnet community, many of the final pieces of today's Internet architecture were falling into place. January 1, 1983, saw the official deployment of TCP/IP as the new standard host protocol for ARPAnet (replacing the NCP protocol). The transition [RFC 801] from NCP to TCP/IP was a "flag day" type event--all hosts were required to transfer over to TCP/IP as of that day. In the late 1980s, important extensions were made to TCP to implement host-based congestion control [Jacobson 1988]. The Domain Name System, used to map between a human-readable Internet name (for example, gaia.cs.umass.edu) and its 32-bit IP address, was also developed [RFC 1034].

Paralleling this development of the ARPAnet (which was for the most part a United States effort), in the early 1980s the French launched the Minitel project, an ambitious plan to bring data networking into everyone's home. Sponsored by the French government, the Minitel system consisted of a public packet-switched network (based on the X.25 protocol suite, which uses virtual circuits), Minitel servers, and inexpensive terminals with built-in low speed modems. The Minitel became a huge success in 1984 when the French government gave away a free Minitel terminal to each French household that wanted one. Minitel sites included free sites--such as a telephone directory site--as well as private sites, which collected a usage-based fee from each user. At its peak in the mid 1990s, it offered more than 20,000 different services, ranging from home banking to specialized research databases. It was used by over 20% of France's population, generated more than $1 billion each year, and created 10,000 jobs. The Minitel was in a large proportion of French homes 10 years before most Americans had ever heard of the Internet. It still enjoys widespread use in France, but is increasingly facing stiff competition from the Internet.

1.9.4: Commercialization and the Web: The 1990s

The 1990s were ushered in with two events that symbolized the continued evolution and the soon-to-arrive commercialization of the Internet. First, ARPAnet, the progenitor of the Internet ceased to exist. MILNET and the Defense Data Network had grown in the 1980s to carry most of the U.S. Department-of-Defense-related traffic and NSFnet had begun to serve as a backbone network connecting regional networks in the United States and national networks overseas. In 1991, NSFNET lifted its restrictions on use of NSFNET for commercial purposes. NSFNET itself would be decommissioned in 1995, with Internet backbone traffic being carried by commercial Internet service providers.

The main event of the 1990s, however, was to be the release of the World Wide Web, which brought the Internet into the homes and businesses of millions and millions of people worldwide. The Web also served as a platform for enabling and deploying hundreds of new applications, including online stock trading and banking, streamed multimedia services, and information retrieval services. For a brief history of the early days of the Web, see [W3C 1995].

The Web was invented at CERN by Tim Berners-Lee in 1989-1991 [Berners-Lee 1989], based on ideas originating in earlier work on hypertext from the 1940s by Bush [Bush 1945] and since the 1960s by Ted Nelson [Ziff-Davis 1998]. Berners-Lee and his associates developed initial versions of HTML, HTTP, a Web server, and a browser--the four key components of the Web. The original CERN browsers only provided a line-mode interface. Around the end of 1992 there were about 200 Web servers in operation, this collection of servers being the tip of the iceberg for what was about to come. At about this time several researchers were developing Web browsers with GUI interfaces, including Marc Andreesen, who led the development of the popular GUI browser Mosaic for X. Andreesen and his colleagues released an alpha version of his browser in 1993, and in 1994 he and James Baker formed Mosaic Communications, which later became Netscape Communications Corporation [Cusumano 1998; Quittner 1998]. By 1995, university students were using Mosaic and Netscape browsers to surf the Web on a daily basis. At about this time companies--big and small--began to operate Web servers and transact commerce over the Web. In 1996, Microsoft got into the Web business in a big way.

During the 1990s, networking research and development also made significant advances in the areas of high-speed routers and routing (see Chapter 4) and local area networks (see Chapter 5). The technical community struggled with the problems of defining and implementing an Internet service model for traffic requiring real-time constraints, such as continuous media applications (see Chapter 6). The need to secure and manage Internet infrastructure (see Chapters 7 and 8) also became of paramount importance as e-commerce applications proliferated and the Internet became a central component of the world's telecommunications infrastructure.